Oxidation ovens are commonly used to produce carbon fibers from a precursor (such as an acrylic, pitch, or cellulose fibers). One common processing method involves successively drawing fibrous segments of the precursor material through one or more oxidation ovens.
Each of the oxidation ovens comprises a respective oxidation chamber in which the oxidation of the fiber segments takes place. Each fibrous segment can be drawn into a first oxidation oven as a carbon fiber precursor and then make multiple passes through each oxidation oven prior to exiting the final oxidation oven as an oxidized fiber segment. Roll stands and tensioners are used to draw the fibrous segments through the oxidation chambers of the ovens. Each oxidation oven heats the segments to a temperature approaching approximately 300° C. by means of a circulating flow of hot gas.
An example of such an oven is the Despatch Carbon Fiber Oxidation Oven, available from Despatch Industries, Minneapolis, Minn. A description of such an oven can be found in commonly-assigned U.S. Pat. No. 4,515,561. The oven described in the '561 Patent is a “center-to-ends” oxidation oven. In a center-to-ends oxidation oven, hot gas is supplied to the oxidation chamber of the oven from the center of the chamber and flows toward the ends of the chamber.
Typically, such a center-to-ends oxidation oven includes a center supply structure located in the center of the chamber. The center supply structure includes a plurality of supply plenums that are stacked one above each other. Gaps are provided between the stacked supply plenums to enable passage of the fibrous segments between the plenums. Each plenum comprises a duct structure that receives heated air through one or both of its ends. Each plenum includes an array of holes formed in each of the opposing side walls of the corresponding duct structure. This array of holes is also referred to here as a “nozzle.” Each plenum is configured to receive heated air and direct the flow of heated gas in approximately horizontal and parallel streams of heated gas out of the nozzles towards both ends of the oxidation chamber.
Such nozzles have typically been formed in a pair of relatively thin metal sheets that form the side walls of the plenum structure. These metal sheets are also referred to here as “nozzle sheets.” FIGS. 1-2 illustrate a portion of one example of a conventional nozzle sheet 100 with nozzles 102 formed in the nozzle sheet 100.
The nozzle sheets 100 typically are less than one-quarter inch thick and are made out of aluminum or similar material suitable for use in an oven. The nozzles 102 are typically formed in each nozzle sheet 100 by perforating the sheet.
Given the relative thinness of such nozzle sheets and the large number of nozzles in the sheets, a sheet of hex honeycomb material has typically been layered on the outer surface of each nozzle sheet in order to reinforce the thin nozzle sheets and to help control the angular direction of the air leaving the nozzles so that it leaves the nozzles in more uniform and parallel streams. FIG. 3 illustrates a portion of a sheet 104 of hex honeycomb material, and FIG. 4 illustrates the hex honeycomb material 104 placed on the outer surface of the nozzle sheet 100 shown in FIGS. 1-2.
However, it can be difficult to precisely align the openings in a sheet of hex material with the corresponding nozzles in a thin nozzle sheet. Misalignment of the openings of the hex material with the nozzles in the nozzle sheet can cause the air leaving the nozzles to do so in less uniform and parallel streams. Also, adding two sheets of the hex material to each plenum increases the cost of manufacturing and assembling each plenum.